Glass grinding machine



H. K. HITCHCOCK GLASS GRINDING MACHINE Filed Feb. 11, 1930 4Sheets-Sheet l R. 0 T N E V m Feb. 21, 1933. H. K. HITCHCOCK Filed Feb.11, 1930 4 Sheets-Sheet P Feb. 21, 1933. H. K. HITCHCOCK 1,898,012

GLASS GRINDING MACHINE Filed Feb. 11 1950 4 Sheets-Sheet 5 F 4 f m \fiz/ INVENTOR Feb. 21, 1933. H. K. HITCHCOCK 1,898,012

GLASS GRINDING MACHINE Filed Feb. 11 1930 4 Sheets-Sheet 4 Patented Feb.21, 1933 UNITED STATES PATENT OFFICE HALBERT K. HITCHCOCK, OFPITTSBURGH, PENNSYLVANIA, 'ASSIGNOR TO PITTSBURGH PLATE GLASS COMPANY, ACORPORATION OF PENNSYLVANIA GLASS GRINDING MACHINE Application filedFebruary 11, 1930. Serial No. 427,583.

19 to such straight away surfacing operation. It has for one of itsobjects the provision of grinding apparatus of the type specified andemploying single runner machines in which a better smooth is securedalong the side edges of the glass sheets than has heretofore beensecured and substantially free from runner scratches along such ecge Afurther object of the invention is the provision of a runner in the useof which the chipping of the glass sheets along their edges is reducedto a minimum. A still further object is the provision of an improvedrunner, the grinding blocks of which are so shaped as to increase thetendency of the abrasive to work therebeneath during the grindingoperation and one in which the area of the runner blocks exposed togrinding contact with the glass is increased as the blocks wear away,thus decreasing the pressure between the glass and the runner blocks perunit of area of the blocks. This is a desirable condition in a system inwhich the runners are shifted progressively as they Wear down from theforward end of the system toward the rear end of the system, as rapidrough grinding is insured, due to relatively hlgh pressure per unit areaof grinding contact at the begin- 4 ning of the operation, combined withfreedom from scratches further along in the grinding operation, due toreduced pressure per unit area of grinding contact in such furthergrinding operation. Certain embodiments of the invention are illustratedin the accompanying drawings, wherein:

Figure 1 is a side elevation showing a part of a grinding systemembodying the invention. Fig. 2 is a diagrammatic plan view.

- Fig. 3 is a partial bottom view of one of the grinding runnersconstructed in accordance with the invention. Fig. 4i is a sideelevation of the construction of Fig. 3. Fig. 5 is a section on the lineV--V of Fig. 3. Fig.- 6 is a section similar to that of Fig. 5 through amodification. Fig. 7 is a. diagrammatic plan view. Fig. 8 is a sectionon the line VIII-VIII of Fig. 7. Fig. 9 is a section similar to that ofFig. 8 after the grinding face of the runner has been worn down. AndFig. 10 is an end elevation partially in section of the construction ofFig. 7.

Referring first to the general arrangement as shown in Fig. 1, 1, 2, 3,l, 5, 6, etc. are a plurality of grinding machines arranged in seriesabove the track 7. Mounted, on the track 7 are a series of tables 8, 8,8, etc. placed end to end in abutting relation and provided on theirlower sides with racks 9 by means of which the tables are fedcontinuously forward from left to right, tables being supplied at theleft hand end of the system as they are removed from the right hand endthereof. The glass sheets to be surfaced are embedded in plaster on thetops of the tables, so that the series of cars constitute in effect acontinuous grinding table. The racks are driven by two spur wheels 9a,96; at the left hand end of the track, such gears being in turn operatedfrom the motors 10, 10 through the spur gears 11, 11 and suitablereduction gearing in the casings 12, 12. The two motors are used merelyto take care of an emergency which might arise due to the failure of asingle drive motor. The grinding machines each comprise a runner frame18 driven from a spindle in the tubular casing 14:, such spindle beingin turn driven from a motor 15 through suitable reduction gearing in thecasing 16. The runner and drive mechanism constitutes a removable unitsuitably counterbalanced and preferably constructed as to detail inaccordance with the machine of the Evans Patent No. 1,577,457. Thedetails of the driving mechanism for the runner constitute no part ofthe present invention, the primary requirement as to this constructionbeing that it may be readily removed from its support so that the unitsmay be shifted from one position in the system to another for thepurpose as hereinafter more fully set forth.

The construction of the runner will be seen by reference to Figs. 3 to7. It comprises a metal frame 13 to the under side of which is secured awood platform 17 which in turn supports the runner bars 18 secured tothe platform 17 by means of the screws 19. The runner bars 18 are ofvarying shape, as will be seen by reference to Fig. 3, which shows fa thof the entire runner bar construction, but each comprises a metal platecarrying from four to thirteen downwardly projecting blocks 20 which areapproximately all of the same shape. These blocks are approximatelytrapesoidal in horizontal cross section and are inclined as indicated inFig. 5. They also preferably increase in horizontal cross section fromtheir lower to their upper ends, as indicated in Fig. 5. In operationsand or other abrasive is supplied near the center of the runner and isdistributed outwardly by centrifugal force through the passagewaysprovided between the runner blocks. The runner is driven in thedirection of the arrows shown in Figs. 8 and 5 so that the sand 21 (Fig.3) directed into the angular spaces between the surface of the glasssheet 22 and the inclined faces 23 of the blocks. Under theseconditions, the sand works under the grinding faces of the runner blocksmuch more effectively than is the case where the side faces of therunner blocks are at right angles to the surface of the glass sheet asis the case in the ordinary runner block construc tion.

The runner blocks 20 are preferably increased in horizontal crosssection from their lower to their upper ends, as indicated in Fig. 5, sothat as the blocks wear down in service, a larger and larger area ofmetal is brought into contact with the glass sheet. This reduces thepressure between the blocks and the glass per unit of area of the blockin contact with the glass. In operating the system, the runners as theybecome worn are shifted from their positions near the forward end of thegrinding system to positions farther along the grinding system. Theabrasive used in the system is supplied in accordance withwell-established practice, the coarsest at the forward end of the systemand becoming gradually finer along the series of tables as the grindingprogresses. At the beginning of the operation, it is desirable to smoothoff the surface of the glass as rapidlv as possible and this is bestaccomplished with the coarsest abrasive upon which a maximum pressure isapplied by the grinding blocks per unit of area of such blocks.Therefore, at the beginning of the operation, runners are employed whoseblocks 20 have not been worn down so that the block area in contact withthe glass is a minimum. Further along in the grinding operation, it isdesirable to smooth the glass without scoring it too deeply by theabrasive and this is better accomplished with the worn runners whosegrinding areas have been increased by the wearing down of blocks such asthose shown in Fig. 5, wherein the cross sectional area increases fromthe lower to the upper ends of the blocks. The runner blocks shown inFig. 5 are, therefore, desirable in carrying out an operation in whichthe runners are shifted after a period of use from the front end of thegrinding system to av position farther along the series. If the runnersare not to be shifted, blocks may be employed like those shown at 20a inFig. 6 in which the cross sectional area of the blocks from their lowerto their upper ends remains constant. In both cases, however, the blocksare inclined as shown so as to provide angular recesses between theforward faces of the blocks and the surface of the glass, thus promotinga movement of the abrasive between the faces of the blocks and theglass.

The peripheral row of grinding blocks 24 (Figs. 3 and 8) have theirouter edges beveled away, as indicated at 25, thus differing from priorconstructions in which the edges of these blocks were formed at rightangles to the surface of the glass sheet being ground. I have found thatthe beveling of the blocks in this manner reduces breakage and chippingat the edges of the glass sheets. This chipping is apt to occur both atthe side edges of the sheet and at the end edges due to the impact ofthe vertical edges of the peripheral blocks. This is particularly liableto occur at the end edges of the sheets where the edge of one sheet maylie slightly above the edge of the succeeding sheet. Under theseconditions, the glass is liable to be chipped when the edge of therunner first strikes the high edge of glass. I have found that bybeveling off the edges of the blocks, as indicated at 25, this chippingaction is reduced to a minimum, since the blow which is struck the edgesof the 7 glass is a glancing or slanting one instead of the morepositive blow which is struck by the edge of a runner which isperpendicular to the surface of the glass.

The beveling of the edges of the runner blocks also has anotheradvantage incident to the system of shifting the runners along the lineof grinding from the front, or rough grinding end, to the rear, orsmoothing end, as heretofore referred to. With runners such as thoseshown in Fig. 7 which extend out past the edges of the glass sheet 22,the grinding effect of the runner is greater along the side edges of theglass sheets than it is along the portions of the sheets intermediate 1such edges. As a result, during the rough grinding, the side edges ofthe sheets are ground down to a slightly lower level than the centralportions of the sheets. The glass during this rough grinding operationis, of course, scored in accordance with the roughness of the abrasiveand it is necessary in the subsequent grinding operation and in thefinal facing of the glass with emery preliminary to polishing to removethe scoring incident to the rough grinding. Since, as above pointed out,the edges of the sheets are ground down somewhat below the level of thecenter portions of the sheets in the rough grinding operation,'in thesubsequent smoothing operations with finer and finer abrasive, therunners do not have the same opportunity to act upon the edge portionsof the glass as upon the center portions, so that when the glass isfinally smoothed with the emery, it is found that the edge portions ofthe sheets do not have the same degree of smooth as the center portions.As a result, in the subsequent polishing operation, great difficulty isexperienced in getting the edges properly polished, a defect beingpresent known as runner scratches, which runner scratches are the tracesof the grinding operation which arenot removed by the polishingmachines. The beveling oil of the edges of the grinders assistsmaterially in eliminating the condition above described, since suchbeveling reduces the diameter of the grinding face of the runner so thatin the coarse grinding operation, the edges are not given the additionalgrinding as above described which brings their level below the level ofthe center portions of the glass. As the grinding continues, the runnersare, of course, worn away and are thus decreased in diameter due to thebeveled edges, this condition being indicated in Fig. 9 which shows oneof the runners after it has been worn down to a considerable extent. Byarranging the runners along the line of grinding so that the runner barsgradually decrease in thickness from the front end of the series to therear end, a condition is secured in which the diameters of the grindingfaces of the runners gradually increase from the rough grinding end ofthe series to the fine grinding or facing end of the series.

This is illustrated diagrammatically in Fig. 2, the difference indiameter of the runners being exaggerated in order to illustrate thecondition described. The runners are originally all of the samethickness and diameter, but in the course of service they become worndown so that it is possible after the grinding is once well under way tosecure the desired gradation in thickness and diameter by progressivelyshifting the runners forward in the series of grinders at certainintervals whose length can be determined by trial, all of the runners 1,2, 3, 4, 5, 6, etc. are shifted ahead one step in the series and a newrunner is added to take the place of the runner 1. Over-grinding of theedges of the sheets is thus avoided in the first portion of the seriesand later in the series the edges are given an increased amount ofgrinding and facing so that any scratches due to the rough grinding areeliminated along the edges of the sheets during the concluding portionof the grinding operation and the smooth secured along the edges of thesheets is made equal to that at their center portions. A comparison ofFigs. 8 and 9 which show sections at the edges of the first and lastrunner respectively indicates clearly the change in diameter of therunners incident to the thinning of the runners by the grindingoperation.

That I claim is:

1. A grinding apparatus for plate glass comprising a series of tablesmounted for right line movement in a continuous train and adapted tocarry the glass sheets to be surfaced upon their upper sides, and aplurality of grinding machines arranged in series above the tables andeach provided with a horizontal driven disc runner whose peripheryprojects out past the side edges of the glass sheets, said runnershaving the diameter of their faces which contact with the glassprogressively larger and larger from the front end of the series onward.

2. A grinding apparatus for plate glass comprising a series of tablesmounted for right line movement in a continuous train and adapted tocarry the glass sheets to be surfaced upon their upper sides, and aplurality of grinding machines arranged in series above the tables andeach provided with a horizontal driven disc runner whose peripheryprojects out past the side edges of the glass sheets, said runners allbeing of the same diameter, but having their corners at the peripheriesof their grinding faces bevelled away, and being of progressively decreasing thickness from the front end of the series on, so that thediameters of the faces of the runners contacting with the glass areprogressively larger and larger from the forward end of the seriesonward.

In testimony whereof, I have hereunto subscribed my name this 29th dayof January, 1930.

H. K. HITCHCOCK.

as the operation continues. In other words, I

